I have not yet turned on the machine, so will update this post with results after the weekend.
I suspect that I will accept the different case (it does look kinda cool – just not sure of the practicalities), and the bonus (although it makes little difference to me actually) of the second DVD writer.
Despite the odd slips as detailed above, I have found cougar to be knowledgeable, helpful polite, answer the phones quickly (unlike some other places), and (subject to updated review of how it all actually works after the weekend) good value as I have a machine built with quality parts that compares well price wise to the alternatives I could find. So despite the slips, I would most certainly deal with them again and recommend them to my friends/family.
As I said, evidence of how companies deal with people when things go wrong is something I was looking for when I started looking round, and so perhaps this will prove useful to someone else in future.